Best-selling "light" cigarettes (9-12 mg tar, by FTC method; Federal Trade Commission, 1990) generally employ filter vents to reduce standard tar and nicotine yields. Earlier research on "ultra light" cigarettes (1-4 mg tar) showed that filter vents were blocked by human smokers leading to dramatic increases in tar and nicotine yields. An objective indicator of vent blocking was applied to a sample of 158 discarded light cigarette butts, and results indicated extreme vent blocking in 47% 27% ( +/- 8, 95% CI), some vent blocking in 26% ( +/- 8), and no vent blocking in 47% ( +/- 8). Cigarette consumers need to be informed of the risks of vent blocking as a countermeasure to the marketing of light cigarettes to health-conscious smokers.